图片缩放时java.lang.IllegalArgumentException: pointerIndex out of range解决方案

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package com.example.webproject;

import android.app.Activity;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.os.Bundle;
import android.util.FloatMath;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class ImageMarixActivity extends Activity{
	private static final String TAG = "ImageMarixActivity";
	private static final int RESULT_CODE_NOFOUND = 200;
	private ImageView matrixImageView;
	

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		setContentView(R.layout.imagemarix_activity);
		matrixImageView = (ImageView) findViewById(R.id.matriximageview);
		//监听图片的触摸事件
		matrixImageView.setOnTouchListener(new TouchListener());
	}
	
	
	public final class TouchListener implements OnTouchListener{
		//记录拖拽是放大还是缩小
		private int mode = 0;//初始状态
		private int DRAG_MODE = 1;//拖拽模式
		private int ZOOM_MODE = 2 ;//缩小模式
		//记录开始的位置
		private PointF startPoint = new PointF();
		//两个手指中间的距离
		private PointF midPont;
		//拖拉图片开始移动的坐标位置
		private Matrix matrix = new Matrix();
		//拖拉图片当前移动的坐标位置
		private Matrix currentMatrix = new Matrix();
		//开始两个手指的距离
		private float twopointstartDis;
		@Override
		public boolean onTouch(View v, MotionEvent event) {
			// TODO Auto-generated method stub
			switch (event.getAction()& MotionEvent.ACTION_MASK) {
			//手指按下的时候
			case MotionEvent.ACTION_DOWN:
				mode = DRAG_MODE;
				//记录当前的位置
				Log.i(TAG, "当前的位置"+matrixImageView.getImageMatrix());
				currentMatrix.set(matrixImageView.getImageMatrix());
				//记录手指按下去的位置
				startPoint.set(event.getX(), event.getY());
				break;
				
			case MotionEvent.ACTION_MOVE:
				Log.i(TAG, "移动"+"模式"+mode);
				//如果是拖拉模式
				if(mode == DRAG_MODE)
				{
					float dx = event.getX() - startPoint.x;
					float dy = event.getY() - startPoint.y;
					matrix.set(currentMatrix);//在原有的基础上移动
					matrix.postTranslate(dx, dy);
				}
				else if(mode == ZOOM_MODE)
				{
					Log.i(TAG, "ZOOM_MODE获取第0个x"+event.getX(0));
					Log.i(TAG, "获取第一个x"+event.getX(1));
					float endDis = distance(event);
					if(endDis >10f)
					{
						matrix.set(currentMatrix);
						float scale =endDis / twopointstartDis;
						matrix.postScale(scale, scale,midPont.x,midPont.y);
					}
				}
				break;
				
			case MotionEvent.ACTION_UP:
				Log.i(TAG, "一只手指点击后弹起来");
//				mode =0;
				break;
				
				
			case MotionEvent.ACTION_POINTER_DOWN:
				mode = ZOOM_MODE;
				twopointstartDis = distance(event);
				if(twopointstartDis>10f)
				{
					midPont = mid(event);
					currentMatrix.set(matrixImageView.getImageMatrix());
				}
				break;
				
			case MotionEvent.ACTION_POINTER_UP:
				Log.i(TAG, "两只手指点击后弹起来");
//				Log.i(TAG, "获取第一个x"+event.getX(1)+"获取的第一个x"+event.getY(0));
//				Log.i(TAG, "获取第一个x"+(event.getX(1)-event.getY(0)));
				mode = 0;
				break;

			default:
				break;
			}
			matrixImageView.setImageMatrix(matrix);
			return true;
		}
		
	}
	
	public float distance(MotionEvent event)
	{
		Log.i(TAG, "调用测距");
		float dx = event.getX(1) - event.getX(0);
		float dy = event.getY(1) - event.getY(0);
		return FloatMath.sqrt(dx*dx+dy*dy);
	}
	
	public PointF mid(MotionEvent event)
	{
		float dx = (event.getX(1)+event.getX(0))/2;
		float dy = (event.getY(1)+event.getY(0))/2;
		return new PointF(dx,dy);
	}

}